Rainfall interception and boundary layer conductance in relation to tree spacing

Abstract

The effect of tree spacing on rainfall interception loss has been investigated in stands of Sitka spruce ( Picea sitchensis (Bong.) Carr) spaced at intervals of 2, 4, 6 and 8 m. The traditional volume balance method was used to measure throughfall, stemflow and interception loss. The variation of throughfall, stemflow and interception loss between the four spacing treatments is analysed. The results obtained showed that, on average, annual intercepton loss as a percentage of gross rainfall was 33, 24, 15 and 9% in the 2, 4, 6 and 8 m spacing treatments, respectively. An estimate of average boundary layer conductance was made by equating interception loss with evaporation rate and inverting a truncated form of the Penman equation. The boundary layer conductance per tree increased with spacing from 0.58 m 3 s −1 in the 2 m spacing treatment to 4.24 m 3 s −1 in the 8 m spacing treatment, whereas boundary layer conductance per unit area declined from 0.17 to 0.07 m s −1 as the density of trees decreased. The difference in interception loss between the spacing treatments was attributed to the difference in the boundary layer conductance.